: ALL MOUTH
AND TROUSERS - "adj. British. Blustering and boastful, showing off without having
the qualities to justify it.There is a suggestion that this is a corruption of
a more logical, but rarely heard expression, 'all mouth and no trousers'. meaning
full of talk but deficient in the sexual area. A less racy version is 'all talk
and no action'. ." From the "Dictionary of Contemporary Slang" by Tony Thorne
(Pantheon Books, New York, 1990).

: On White Oak Mountain in W.Va., we called
a boastful person a "blow George." In Texas, it is "all hat and no cattle."

"All
mouth and trousers" and "all mouth, no trousers" are both still used interchangeably
in the UK today, both meaning as described by previous posters.

Very similar
expressions would be "blowhard" (archaic), "all talk, no action" or "he talks
the talk but don't (sic)/can't walk the walk", which we've inherited from the
US.